34 PROGRESS OF SCIENCE. 



the motions of the sun, moon, and planets, held in high 

 repute for centuries ; measured the obliquity of the ecliptic 

 in 879 the result being 23 35' o". 



875. Thebit Ben Corrah found out the exact length of 

 the YEAR: 365 days 5 hours 48 min. n sec. As an 

 anatomist he described the ANATOMY OF BIRDS. 



975. Aboul Wefa observed at Bagdad the third IN- 

 EQUALITY OF THE MOON (viz., the variation], by virtue of 

 which our satellite moves quickest when she is at new and 

 full ; but he failed to fix the law. This inequality was re- 

 discovered by Tycho Brahe. He also measured the obliquity 

 of the ecliptic in 987 (the result being 23 35' o"). 



995. Aboul Rihau measured the obliquity of the ecliptic 

 with a QUADRANT of 25 feet radius in 995 (the result 

 2335'o"). 



1008. Ebn Junis applied mathematics, using algebra 

 and the Arabic numerals in his calculations, in the solution 

 of physical and astronomical problems ; drew up the 

 HAKEMITE TABLES ; achieved the most valuable of chrono- 

 metric improvements by applying the PENDULUM to the 

 measure of time. The value of his work is proved by the 

 fact of Laplace making use of his astronomical observations 

 as an evidence of the diminution of the eccentricity of the 

 earth's orbit. 



1080. Arzachael measured the OBLIQUITY OF THE 

 ECLIPTIC (the result being 23 34' o"). 



Aboul Hassan used tubes for astronomical observations 

 to which ocular and object diopters were fixed and which 

 were a near approach to the invention of THE TELESCOPE. 



Sufi (Abderrahman) improved the PHOTOMETRY of the 

 stars a feat which we should have expected to be reserved 

 only for modern science to accomplish. 



1198. Geber of Seville constructed the OBSERVATORY of 

 that city the earliest in Europe and the most complete on 

 record. It was turned into a belfry after the expulsion of 

 the Moors, " the Spaniards not knowing what to do with it." 

 1259. Tasi (Nessar Eddin) drew up the ILKANIC TABLES 

 at the observatory of Meragha (near Tauris). 



I 394 1449- Ulugh Begh (Prince) by means of a 



